The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
The present invention relates generally to a spectropolarimetric reflectometer for measuring the polarization characteristics of materials in reflection over broad wavelength regions.
Many sensor systems rely on reflected light, from natural or manmade sources, to obtain the energy for their detector elements. The ability of the sensor system to detect and process reflected energy depends on knowledge of the reflection characteristics, including polarization properties, of the materials. An instrument is therefore needed that measures the polarization of reflected light over broad regions of the ultraviolet (UV), the visible and infrared (IR) spectrum in order to evaluate polarized reflection properties of materials.
Relevant prior art instrumentation includes an infrared spectropolarimeter for measuring polarization properties of materials in transmission, as described by Goldstein et al (U.S. Pat. No. 5,045,701 (Sep. 3, 1991)), the entire contents of which are incorporated by reference herein. The Goldstein et al ""701 spectropolarimeter is based on a Fourier transform infrared spectrometer containing a dual rotating retarder Mueller matrix polarimeter in the sample compartment. Measurements can be made of polarization properties of transmissive samples over large wavelength regions into the infrared (2.5 xcexcm and further into the IR).
The invention solves or substantially reduces in critical importance problems with prior art instruments by providing a polarimeter incorporating a modem Fourier transform spectrometer (FTS) that is capable of measurements over broad spectral regions from the UV to the far IR of samples in reflection, and is capable of rapid collection of more spectral and polarimetric information, primarily in the form of Mueller matrices, mathematical functions that completely describe the polarization properties of a sample, for each wavelength collected by the spectrometer, than any known instrument. The invention has substantial use in a broad range of applications, including electrooptic sensors, robotic vision, laser cutting and welding, and telecommunications.
It is therefore a principal object of the invention to provide a novel polarimeter.
It is another object of the invention to provide an instrument for measuring the polarization characteristics of materials in reflection over broad spectral wavelength regions.
It is a further object of the invention to provide a spectropolarimetric reflectometer operating over broad wavelength regions from the ultraviolet to the far infrared.
It is yet another object of the invention to provide an instrument for generating Mueller matrix functions describing the polarization properties of materials in reflection.
These and other objects of the invention will become apparent as the detailed description of representative embodiments proceeds.
In accordance with the foregoing principles and objects of the invention, a spectropolarimetric reflectometer for measuring polarimetric reflection properties of materials over broad spectral wavelength regions is described wherein radiation from a Fourier transform spectrometer passes through a set of polarization elements that serve as a polarization state generator and is reflected off the sample and collected by optics that includes a polarization state analyzer, focusing mirror and detector.